Would you start low dose methimazole therapy in patients with positive TRAb, normal FT4 and FT3 levels but ongoing TSH suppression in a completely asymptomatic young patient?  

Yes, if TSH is <0.1, I would start Methimazole. The TRAb indicate higher risk of progressing to overt hyperthyroidism.As per European Thyroid guidelines, you can consider it, but it is at clinician's discretion: "Endogenous mild or subclinical hyperthyroidism (SH) is associated with increased ris...